The present invention relates to improvements in methods of and in apparatus for testing containers, especially bottles which are made of glass or a synthetic plastic material. More particularly, the invention relates to improvements in methods of and in apparatus for testing containers (hereinafter called bottles for short) with beams of optical radiation. Still more particularly, the invention relates to improvements in methods of and in apparatus for optically testing preferably colorless bottles which transmit radiation and are transported through a testing station wherein a selected portion of the surface of each of a series of successive bottles is positioned to influence a beam of radiation so that the changes in the characteristics of such beam can be resorted to for the determination of one or more qualities of the tested bottle.
The beverage making and bottling industries utilize large numbers of plastic bottles, particularly those made of polyethylene terephthalate (PET). An advantage of such bottles is that they can be mass-produced with smooth internal surfaces. However, such bottles also exhibit a drawback, namely that they are capable of swelling. Such characteristics of a bottle which is made of PET are undesirable because various chemical substances whose chemical composition is similar to that of PET are likely to penetrate into the material of the bottle close to the internal surface and to settle between the long-chain molecules of the plastic material. This creates problems when a PET bottle is thereupon filled with a flowable substance, such as a beverage, containing one or more materials whose composition is similar to that of PET. For example, if a bottle was utilized to store waste oil, benzine or a herbicide, such substances (or certain constituents of such substances) are likely to be diffused and to settle in the intermolecular spaces within a wall of the bottle. If the same bottle is thereupon put to use as a means for storing a metered quantity of a beverage, even after very thorough cleaning prior to admission of the beverage, the diffused substances are likely to leave the intermolecular spaces and to render the confined beverage undrinkable or even dangerous to the health of the consumer. Furthermore, aromatic substances which are contained in fruit juices or other aromatized beverages are likely to penetrate into the wall of a PET bottle. This is not, or need not be, harmful or undesirable if the bottle is thereupon filled with the same beverage. However, the aromatic substances which have penetrated into the wall of a bottle are likely to undesirably affect the taste of a different beverage which is introduced into the same bottle subsequent to cleaning. Aromatic substances which have penetrated into the wall of a bottle are particularly likely to affect the taste of mineral water if such liquid is introduced into a bottle which was previously filled with a fruit juice or with an aromatized beverage. Even minute traces of an aromatic substance which was permitted to penetrate into the wall of a PET bottle and thereupon contacts a supply of mineral water are likely to impart to the mineral water a taste which need not necessarily be unpleasant but is nevertheless not to the liking of a person who desires to drink genuine mineral water.
Heretofore known bottle cleaning apparatus are incapable of properly and reliably cleaning bottles having walls wherein the intermolecular spaces are filled with diffused aromatic substances or with any other substances which are likely to enter a supply of beverage in the freshly cleaned bottle. On the other hand, it is not only desirable but also important and often critical to ensure that a bottle whose walls contain substances which are likely to contaminate a freshly introduced supply of liquid can be detected and segregated from satisfactory bottles. Therefore, the bottle filling industries employ a variety of inspecting apparatus which are intended to detect undesirable (including dangerous) substances (such as contaminants) and to thus ensure reliable segregation of unacceptable bottles from satisfactory bottles. For example, it is known to direct one or more beams of radiation against a bottle in such a way that the beam or beams penetrate through the opening and through the bottom end wall of the tested bottle. The intensity of a beam which issues from the bottle is monitored in order to draw conclusions regarding the quality of the tested container. Such procedure is satisfactory if one desires to ascertain the presence of relatively large foreign bodies, the presence of one or more contaminants and/or the presence of defects (e.g., damage to the internal surface of the bottom wall). However, minor defects are not likely to be detected by resorting to heretofore known inspecting apparatus. Moreover, such apparatus are incapable of detecting the presence of traces of undesirable substances which adhere to the internal surface of a plastic bottle or which have become diffused in the spaces between the molecules of plastic material adjacent the internal surface of a bottle. This also holds true for certain recent proposals (known as sniffing methods) which are intended to permit detection of substances likely to release aerosols in a plastic bottle. Moreover, such methods cannot be resorted to in connection with the testing of bottles in a high-speed bottle filling machine because the testing of a bottle takes up a relatively long interval of time. Still further, the reliability of such methods is questionable so that they cannot be resorted to in connection with the testing of bottles which are about to receive beverages and/or other substances intended for consumption by humans or animals.